1. Field of the Invention
The present invention relates to a binder composition for mortars and enhanced coatings, comprising a first conventional mineral component and a second component based on powdered slaked lime.
2. Description of the Prior Art
By the term of <<mortar>> is meant in the sense of the present invention, a mixture of one or several mineral binders like lime, a cement or the like and of aggregates, mainly sand; this is then a traditional mortar. Such a mortar is used in building for binding and/or for covering the building elements and may also contain fillers, one or several organic binders, additives and/or adjuvants. A mortar with high added value or highly added, for which the composition and the manufacturing are defined in order to obtain specific properties, may be described as enhanced or performing or further formulated (designed mortar). Are notably included therein adhesive mortars, self-leveling floors, screeds, repair mortars, certain masonry mortars, etc. . . .
By the term of <<coating>>, is meant a mortar composition intended to be applied as a layer in one or several passes. A coating is therefore a mortar for outdoor surface application (render) or indoor surface application (plaster).
The mortars and coatings may be made up from formulations of binders with hydraulic, pozzolanic or air setting, or from their mixture. The use of air lime or slaked lime has advantages as compared with binders without lime: better plasticity having as a result better handling capability/applicability, better retention of water which allows improved tolerance towards variations in the porosity of the support, better permeability to water vapor, and better flexibility of the cured system.
Moreover, it is well known that in enhanced (also called performing or formulated) mortars and coatings, the addition of additives, notably organic additives, is a preferred method for purposes of optimizing application performances.
Slaked lime consists of a set of solid particles, mainly calcium di-hydroxide of formula Ca(OH)2, and is the industrial result of slaking of quick lime with water, in a reaction also called a hydration. This product is also known as hydrated lime or air lime and typically has BET surface areas of the order of 15 to 20 m2/g (J. A. H. Oates, Lime and Limestone—Chemistry and Technology, Production and Uses, 1998, p. 220).
This slaked or hydrated lime or air lime or calcium hydroxide may of course contain impurities, i.e. phases derived from SiO2, Al2O3, Fe2O3, MnO, P2O5, K2O and/or SO3, globally representing a few tens of grams per kilogram. Nevertheless, the sum of these impurities, expressed as the aforementioned oxides, does not exceed 5% by mass, preferably 3%, preferably 2% or even 1% of the mass of the slaked lime according to the invention. In particular, the slaked lime advantageously contains less than 1.5% by mass of Fe2O3, preferably less than 1% and preferably less than 0.3%.
Such slaked lime may contain magnesium oxide and/or hydroxide. Depending on the contents of these compounds, the lime will be referred to as magnesium, dolomitic or dolomite lime, either partly or totally slaked.
This slaked lime may also contain calcium oxide which would not have been hydrated during the slaking or stemming from non-uniform baking (localized over-baking), just as it may contain calcium carbonate CaCO3 or magnesium carbonate MgCO3. These carbonates may stem either from the initial limestone (or from the crude dolomite), from which is derived the slaked lime according to the invention (not baked), or from a partial carbonation reaction of the slaked lime in contact with air. The calcium oxide content in the slaked lime within the scope of the present invention is generally less than 5% by mass, preferably less than 2% and advantageously less than 1%. That of carbonates is less than 10% by mass, preferably less than 6% and advantageously less than 4%, still more advantageously less than 3%.
In the technical field of lime mortars and coatings, with the purpose of improving the aforementioned properties, existing teachings for example propose operating on the specific surface area and in reality disclose many results quite different from each other.
For example, document WO 2008034616 discloses that it is possible to accelerate the development of compressive forces of binder compositions with hydraulic setting by adding lime with a particular specific surface area.
The targeted specific surface area in this document is comprised between 7 and 16 m2/g and the preferential embodiments are directed to slaked limes having a specific surface area comprised between 11 and 14 m2/g for lime contents of about 5% by weight based on the total weight of the binder (Portland cement).
Document BE 1006309 as for it teaches the use of a method for increasing the specific surface area and the plastic properties of the hydrated lime, in particular with a chemical modification agent in order to give it a much higher specific surface area. This object of this invention is further a hydrated lime having a much greater capability of retaining water and of becoming more plastic. In this way, the thereby produced slaked lime may be used in mortars in smaller proportions while allowing the latter to retain the workability required by codes or standards.
According to document DE 102005018100, calcium hydroxide with great fineness is used for producing hydraulic mortars or binders for producing concretes having improved flow and setting characteristics. This calcium hydroxide with great fineness typically has both high BET and Blaine specific surface areas.
Further, document WO 9209528 provides the use of calcium hydroxide or slaked lime as milks or slurries of Ca(OH)2 and/or Ca(OH)2—Mg(OH)2 in the building industry for making mortars, coatings, etc. . . . This document teaches that the quality of the Ca(OH)2 milks and/or slurries, optionally mixed with Mg(OH)2, and their property, for example their reactivity, depend on the dimension and the structure of the agglomerates or micelles of suspended Ca(OH)2 and/or Ca(OH)2—Mg(OH)2. The conclusion of this document is in reality that the particles of Ca(OH)2 and/or Ca(OH)2—Mg(OH)2 of the agglomerates or micelles should have a small grain size and large porosity in order to obtain a highly reactive milk or slurry and for reducing or avoiding sedimentation of the particles. Still according to this document, in the case of slurries, with a small grain size and large porosity it is possible to obtain mortars having high plasticity and a high power of retaining water.
Accordingly, it appears that, with the purpose of having the high plasticity required of coatings and enhanced mortars, as well as the water retention power required for application on any type of surface, a slaked lime with a high specific surface area must rather be selected.
In spite of the aforementioned advantages, the use of binders based on slaked lime also generates some drawbacks such as for example the requirement of using high contents of organic additives typically present in the enhanced mortars and coatings and for which the role is to ensure specific functions such as retention of water, management of the flow properties (handling capability/plasticity, castability, flow threshold, . . . ), adherence, abrasion resistance, hydrophobicization or further air entrainment.